FIG. 1 shows a block diagram of a conventional battery charging circuit 100. As shown in FIG. 1, the battery charging circuit 100 is implemented by an adapter 102, a pulse width modulation controller 108, a charger controller 110, and a battery protection circuit (not shown) in the battery pack 104. The adapter 102 outputs a fixed voltage, and a charger 106 (shown as the pulse width modulation controller 108 and the charger controller 110) steps down the output voltage of the adapter 102 by controlling power switches and a buck converter in block 112. Consequently, conventional battery charging circuits can be relatively large and costly.
FIG. 2 shows a block diagram of another conventional charging circuit 200. The charging circuit 200 includes a controllable adapter 202 and an external control chip shown as a charger controller 210. The external control chip (charger controller 210) controls an output power of the controllable adapter 202 according to a current/voltage of the battery pack 204. As shown in FIG. 2, the charging circuit 200 also needs an extra switch 212 to control a charging current of the battery pack 204. As a result, such battery charging circuits are also relatively large and costly.
Furthermore, in conventional charging circuits, due to unbalancing issues (e.g., cells in the battery pack may have different voltages/capacities), some cells may reach an over-voltage condition even though others have not yet been fully charged. In other words, the charging process may not be accurate enough across all of the cells.